Aiming at the issue of inter-shaft bearing waviness in a dual rotor system， the dual rotor-bearing system of external rotor with variable cross section was taken as the research case. The dynamic model of the dual rotor-bearing system was established based on the Finite Element Modeling （FEM）. The waviness of the inner and outer ring raceways and the rolling body of the intershaft bearing were considered in the model. The fourth order Runge-Kutta numerical method was used to solve the equations， and the influence of waviness excitation on the amplitude-frequency response curve and spectral characteristics of the system was ana? lyzed. The results show that when there is waviness in the inner and outer ring raceways， the system exhibits a combination fre? quency of the inner and outer rotor rotation speed frequency as well as cage rotation speed frequency. And when there is waviness in the rolling body， the system has an even times of the rolling body self-rotation speed frequency. When the rotor is unbalanced， the outer ring raceway waviness will amplify vibrations in the resonance region of the outer rotor main excitation. The vibration of the system will increase in the whole speed range with the increase of the waviness amplitude， while the vibration responses of the inner ring raceway waviness and the unbalanced excitation will appear similar to the same frequency and reverse phase phenomenon in the second resonance region of the inner rotor main excitation. The vibration of the system will decrease with the increase of wav? iness amplitude， while the vibration in other regions will increase. Compared with the high rotating speed region， the waviness of the rolling body significantly impacts on the vibration characteristics in the low rotating speed region.